As discussed in Ref. [1]}, the four-quark local operators \(O_{1,4.5}\) 
can be treated at low energy in chiral EFT.
The discussion of \(O_1\)  is given in Section REF  and we focus here on \(O_{4,5}\) .
At LO only non-derivative four-nucleon and pion–pion vertices appear,
\(O_{4,5} \ \rightarrow \ g_{4,5}^{NN} \, \bar{p} n \bar{p} n\ + \ \frac{1}{2} g_{4,5}^{\pi \pi } \, F_\pi ^2 \, \pi ^- \pi ^- \, + \ldots \) 
